1. Field of the Invention
This invention relates generally to shield connections for tunnel valve sensors, and more particularly to shield connections formed by connecting columns that are magnetically uncoupled from the shields.
2. Description of the Related Art
Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (e.g. a disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially-spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive (MR) read sensors, commonly referred to as MR sensors, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater track and linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an xe2x80x9cMR elementxe2x80x9d) as a function of the strength and direction of the magnetic flux being sensed by the MR layer. The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization in the MR element and the direction of sense current flowing through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers. Sensors using only two layers of ferromagnetic material (e.g., NiFe) separated by a layer of non-magnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors manifesting the SV effect.
Another type of magnetic device is a magnetic tunnel junction (MTJ) device or xe2x80x9ctunnel valve sensorxe2x80x9d. The MTJ device has potential applications as a memory cell and as a magnetic field sensor. The MTJ device comprises two ferromagnetic layers separated by a thin, electrically insulating, tunnel barrier layer. The tunnel barrier layer is sufficiently thin that quantum-mechanical tunneling of charge carriers occurs between the ferromagnetic layers. The tunneling process is electron spin dependent, which means that the tunneling current across the junction depends on the spin-dependent electronic properties of the ferromagnetic materials and is a function of the relative orientation of the magnetic moments, or magnetization directions, of the two ferromagnetic layers. In the MTJ sensor, one ferromagnetic layer has its magnetic moment fixed, or pinned, and the other ferromagnetic layer has its magnetic moment free to rotate in response to an external magnetic field from the recording medium (the signal field). When an electric potential is applied between the two ferromagnetic layers, the sensor resistance is a function of the tunneling current across the insulating layer between the ferromagnetic layers. Since the tunneling current that flows perpendicularly through the tunnel barrier layer depends on the relative magnetization directions of the two ferromagnetic layers, recorded data can be read from a magnetic medium because the signal field causes a change of direction of magnetization of the free layer, which in turn causes a change in resistance of the MTJ sensor and a change in the sensed current or voltage. IBM""s U.S. Pat. No. 5,650,958 granted to Gallagher et al., incorporated in its entirety herein by reference, discloses an MTJ sensor operating on the basis of the magnetic tunnel junction effect.
The electrical sense current to the MTJ sensor is preferably applied by means of electrical conductors in the form of thin metal layers located above and below the MTJ sensor. More particularly, the magnetoresistive read elements are typically placed between two thick and highly permeable magnetic layers or xe2x80x9cshieldsxe2x80x9d. The shields may be connected to read signal processing circuitry through what are referred to as xe2x80x9cconnecting columnsxe2x80x9d made of a magnetic material. Unfortunately, such connecting columns for the shields may undesirably influence the magnetic properties of the shields, which may result in magnetic instability for the shields.
To further illustrate, FIG. 1 shows a top down view of a partially constructed magnetic head 100. In FIG. 2, a cross-sectional view along lines IIxe2x80x94II of FIG. 1 of this magnetic head is shown, and in FIG. 3 a more completed magnetic head is shown in cross-section. Magnetic head 100 includes a first shield 102 and a second shield 104, both made of a magnetic material. A tunnel valve sensor 106 is sandwiched in between and coupled to these first and second shields 102 and 104.
A first connecting pedestal 110 helps provide a first connection for sensor 106 from first shield 102, whereas a second connecting pedestal 112 helps provide a second connection for sensor 106 from second shield 104. First and second connecting pedestals 110 and 112 are made of a magnetic material. Also, first connecting pedestal 110 is formed over first shield 102 along its back edge and, similarly, second connecting pedestal 112 is formed over second shield 104 along its back edge. Connecting pedestals 110 and 112 are extended upwards to form connecting columns. These connecting columns are coupled to read pads on the surface of the slider; leads are wire-bonded to these read pads and coupled to read signal processing circuitry of the disk drive. Remaining conventional elements of the magnetic head in FIG. 3 include a first pole piece (P1) layer 108, a P1 pedestal 306, a P1 back gap pedestal 318, a second pole piece (P2) which includes a P2 pole 310 and a P2 back gap 316, a gap layer 310 which separates the first and the second pole pieces at the ABS, a connecting yoke 312, and write coils 314. First pole piece layer 108, P1 pedestal 306, P1 back gap pedestal 318, P2 pole 310, P2 back gap 316, and connecting yoke 312 are made of magnetic materials, whereas gap layer 310 is made of an insulator.
The basic problem is that the connecting columns may adversely affect the magnetic behavior of the shields. This is due to stress contributions. It may be desirable that at least portions of the connecting columns be made from a magnetic material that is different from the magnetic material of the shields. For example, it may be desirable to make the upper layers of the connecting columns from the same magnetic material as the pole pieces. The use of additional connecting layers results in an even stronger influence on the magnetic properties of the shield, which may undesirably lead to magnetic instabilities in the shield.
Accordingly, what are needed are improved shield connections for tunnel valve sensors in magnetic heads and methods of making the same.
The present invention relates to a magnetic head which includes a tunnel valve sensor, a first shield coupled to a first end of the tunnel valve sensor, and a second shield coupled to a second end of the tunnel valve sensor. A first connecting column of the magnetic head electrically couples the first shield to a first read pad, and a second connecting column of the magnetic head electrically couples the second shield to a second read pad. The first connecting column is magnetically uncoupled from the first shield and the second connecting column is magnetically uncoupled from the second shield. Advantageously, this eliminates or substantially reduces the influence of the connecting columns on the magnetic properties of the shields.
In one embodiment of the invention, the first connecting column is offset from the first shield and is coupled to it through a first connecting neck. Similarly, the second connecting column is offset from the second shield and is coupled to it through a second connecting neck. Preferably, the upper layers of the first and second connecting columns are made of the same conductive magnetic material as first and second pole pieces, which reduces the processing steps required in making the magnetic head. In an alternate embodiment of the invention, the first and the second shields are made of a magnetic material whereas the first and the second connecting columns are made of a non-magnetic electrically conductive material (e.g. copper). Here, the first and the second connecting columns may be formed over the shields or be offset from the shields and coupled thereto via connecting necks.
Advantageously, connecting columns which provide electrical connections for the tunnel valve sensor do not influence the magnetic properties of the shields in any significant way, and may be constructed using a simplified process.